This invention relates to communication in environments where interference from signals relating to one communication protocol can hinder the reception of signals relating to another communication protocol.
One example of such an environment is when transceivers for two protocols that occupy the same or adjacent frequency bands are located close to each other or even in the same device: for instance a handheld communication device. As an example, a transceiver for IEEE 802.11a/j wireless LAN (local area network) signals could be located near to or in the same device as a transceiver for Ultra-Wideband (UWB) signals. Some combinations of IEEE 802.11a/j and Ultra-Wideband channels, even those that only partially overlap in frequency bandwidth, resulting in mutual interference between the two protocols. Because of this mutual interference it is desirable to adopt a coexistence scheme that enhances the ability of a receiver for one of those protocols to operate in the presence of interference from signals of the other protocol.
The IEEE 802.11 standard is defined in the following documents, among others: IEEE Computer Society, IEEE Standard for Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, IEEE Std 802.11™—2007 (Jun. 12, 2007); IEEE Computer Society, Supplement to IEEE Standard for Information technology—Telecommunications and information exchange between Systems—Local and metropolitan area networks—Specific requirement—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications—High-speed Physical Layer in the 5 GHz Band, IEEE Std 802.11a-1999(R2003) (Jun. 12, 2003); and IEEE Computer Society, IEEE Standard for Information technology—Telecommunications and information—exchange between systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications—Amendment 4: Further Higher Data Rate Extension in the 2.4 GHz Band, IEEE Std 802.11g™-2003 (Jun. 27, 2003). All these documents are incorporated herein by reference. As used herein, an IEEE 802.11 radio, transceiver or protocol is a radio, transceiver or protocol that conforms in relevant respects to the 2007 standard above, whether or not it also conforms to either 2003 standard above or any other version of the IEEE 802.11 standard.
There are many known coexistence schemes that allow Bluetooth and IEEE 802.11 to coexist. These include the 2-wire and 3-wire de-facto industry standard coexistence signaling systems, described by documents. The 3-wire standard is shown in PCT applications WO/2006/090242 and WO/2006/090254. However, these coexistence schemes were designed to operate with Bluetooth and cannot simply be used with a UWB radio to allow UWB and IEEE 802.11 to coexist as the nature of UWB transmission and reception is different to that of Bluetooth. Therefore, there is a need for a method of allowing a UWB radio to be used with existing Bluetooth coexistence enabled IEEE 802.11 hardware.
The Bluetooth standard is defined in Bluetooth SIG, Specification of the Bluetooth System, v2.1+EDR (Jul. 26, 2007), incorporated herein by reference. As used herein, a Bluetooth radio, transaction, slot or protocol is a radio, transaction, slot or protocol which conforms in relevant respects to this specification, whether or not it also conforms to other versions of such specification.
An IEEE 802.11 radio operates on a frequency-static channel that can be on one of 14 channels within the range 2400-2480 MHz for IEEE 802.11b/g (same as Bluetooth) or on one of many channels within the range 4900-5850 MHz for IEEE 802.11a/j. The effect of the two radios on each other's operation will depend on the degree to which their channels are separated by frequency difference between their channels and the relative strength of each signal. The closer the channels are, the greater the interference and the stronger one signal is, the more the other signal will suffer from interference.
The UWB specification is defined by the WiMedia Alliance MultiBand OFDM Physical Later Specification or ‘ECMA-368’. It is defined in ECMA International, High Rate Ultra Wideband PHY and MAC Standard, 3rd ed. (December 2008) and in ECMA International, High Rate Ultra Wideband PHY and MAC Standard, 2nd ed. (December 2007), both of which are incorporated by reference herein. As used herein, the term Ultra-wideband radio, transceiver, protocol, beacon, reservation, transmission, preamble or activity is any radio, transceiver, protocol, beacon, reservation, transmission, preamble or activity that conforms to the relevant aspects of the ECMA-368 specification, 2nd edition, whether or not it also conforms to the 3rd edition or any subsequent revision of that specification.
ECMA-368 defines 6 Band Groups within which the UWB radio can operate; Band Group 1 defines a frequency bandwidth of between 3168 MHz and 4752 MHz, Band Group 2 defines a bandwidth of between 4752 MHz and 6336 MHz, Band Group 3 defines a bandwidth of between 6336 MHz and 7920 MHz, Band Group 4 defines a bandwidth of between 7920 MHz and 9504 MHz, and Band Group 5 defines a bandwidth of between 9504 MHz and 10560 MHz. Band Group 6 operates between 7392 MHz and 8976 MHz, i.e. it overlaps Band Groups 3 and 4.
Current UWB devices are Band Group 1, but future UWB devices used as higher-speed radios for Bluetooth will use frequencies above 6 GHz, due to concerns from cellular phone companies that UWB would interfere with WiMAX or other cellular radios. The Bluetooth SIG are mandating operation above 6 GHz, but some devices may continue using Band Group 1 due to either performance or compatibility reasons.
Due to both regulatory constraints and those from other organisations (such as the WiMedia Alliance and the Bluetooth SIG), any particular selection of intercommunicating UWB radios are unlikely to have any choice regarding the Band Group that they respectively use. There will usually be a choice of Band Group for new connections, although it will often be limited. However, if there is a pre-existing beacon group then new devices will often adopt its channel (Band Group and hopping sequence) rather than selecting their own. They may, however, have an option to select the hopping sequence—where one of the options is to stay on a single band (at a lower power level) rather than spreading the signal across three bands. There are also hopping sequences that use any two of the three bands in a Band Group.
In the case of a UWB receiver using Band Group 1, as an example, a greater than +5 dBm IEEE 802.11b/g signal might prevent UWB reception, as might a greater than −12 dBm IEEE 802.11a signal. Assuming 20 dB antenna isolation between the UWB and IEEE 802.11 antennas and a 20 dBm IEEE 802.11 output power this would mean that an IEEE 802.11b/g transmitter would not cause interference problems for the UWB receiver unit but an IEEE 802.11a transmitter would block the UWB receiver from receiving. A Band Group 2 UWB radio would suffer even worse from IEEE 802.11a transmissions. On the other hand, a Band Group 5 radio would be unlikely to have any problems.
FIG. 1 shows a hardware arrangement according to the prior art which uses more than one radio protocol. The system comprises a transceiver 1 for sending and receiving signals according to a first radio protocol and transceiver 2 for sending and receiving signals according to a second radio protocol. The transceiver 1 and transceiver 2 are co-located in a device 100.
In FIG. 1, the first radio protocol is IEEE 802.11 and the second radio protocol is Bluetooth. In the Bluetooth protocol, the timings of transmission of signals by the transmitter 2 can be influenced and varied during operation.
Transceiver 1 and transceiver 2 are connected using a ‘2-wire’ coexistence scheme. This consists of two single bit data means 3 and 4, which allow transceivers 1 and 2 to exchange data regarding their respective current transmission and reception activities. By enforcing a set of rules which dictate behavior of the respective radio transceivers based on the high or low assertions of the single bit data means, transmissions from one transceiver which conflict with the transmission or reception of the other transceiver can be avoided.
The ‘2-wire’ coexistence scheme, as shown in FIG. 1, is the simplest common coexistence signaling scheme, and uses two wires most commonly called WLAN_Active and BT_Priority respectively:                BT_Priority (3) is asserted by the Bluetooth radio whenever it is receiving (or optionally when transmitting) a packet that it considers to be high priority. Anything other than bulk data is normally considered to be high priority; this includes device discovery, connection creation, link maintenance, and voice traffic.        WLAN_Active (4) is asserted by the IEEE 802.11 radio whenever it is receiving or transmitting. Some implementations assert this signal whenever the radio is not in power-save, but others only assert it during actual packet reception or transmission.        
FIG. 2 shows a similar hardware arrangement to that shown in FIG. 1. However, in FIG. 2, transceiver 1 and transceiver 2 are connected using a ‘3-wire’ coexistence scheme (or ‘4-wire’ if BT_InBand is implemented). This consists of three single bit data signaling means 10, 11, and 12 (and 13 if you include the BT_InBand data signaling means), which allow transceivers 1 and 2 to exchange data regarding their respective next or current transmission and reception activities. As per the ‘2-wire’ scheme, by enforcing a set of rules which dictate behavior of the respective radio transceivers based on transitions and levels of the data means, transmissions from one transceiver which conflict with the transmission or reception of the other transceiver can be avoided.
The ‘3-wire’ coexistence scheme, as shown in FIG. 2, is the most common coexistence signaling scheme and comprises an IEEE 802.11 radio and a Bluetooth radio, and uses three wires, which will be called here BT_Active, BT_Status and WLAN_Active. These are occasionally supplemented by a fourth wire which will be called BT_InBand:                BT_Active (12) is asserted for Bluetooth transactions.        BT_Status (11) provides information about the priority and direction (transmit or receive) of the Bluetooth activity.        BT_InBand (13), if present, indicates whether the Bluetooth activity is on a frequency that overlaps the channel being used by the IEEE 802.11 radio.        WLAN_Active (10) is asserted by the IEEE 802.11 radio to prevent the Bluetooth radio from transmitting. Some implementations assert this continuously when the IEEE 802.11 radio is active, but others only drive it in response to BT_Active being asserted.UWB Transmit and Receive Activity        
There are two main types of activity according to the UWB protocol that benefit from protection from interference from another transceiver using a different protocol:
Beacons—Every 65 ms there is a beacon that is composed of transmissions from all devices in the UWB network. These may vary in length from 0.2 ms to >20 ms depending on the number of devices in the network. If three successive beacons are not received by a particular device then the device will drop its connection, so it is very important that this does not occur.
Reservations—Each beacon reserves slots for particular devices to exchange data. If a device has only reserved a very few slots then it is important that the device gets to use those particular slots otherwise no data transfer will occur. This method is formally referred to as Distributed Reservation Protocol (DRP). Another method is known as Prioritized Contention Access (PCA). The PCA approach allows any device to content for access to the medium (in a similar manner to IEEE 802.11) whenever it has not been reserved, but this is less efficient (the radios have to remain active) and this mode is not used by systems such as Wireless USB.